"I can't find one person who has been using the Nexus 7 for an extended period of time, and hasn't seen a massive downgrade in performance. Just what kind of downgrade are we talking here? I cannot pick up my Nexus 7 without experiencing problems like a lag of ten seconds, or more, just to rotate the display; touches refusing to acknowledged; stuttering notification panel actions; and unresponsive apps." Fully and utterly agreed. My Nexus 7 was blazing-fast and awesome for a few months, and at some point, it just started sucking. Just like that. I've tried loads of ROMs, and nothing helps.

Risking an OS war a bit, but shouldn't a mobile OS (like Android) have a filesystem designed specifically for flash storage (with a trim command and all), instead of using a filesystem designed for spin-up magnetic drives (ext4), and ask from the hardware to emulate a spin-up magnetic drive for it?

Really, I don't think it's fair to single out Android on this front. iOS is BSD-based, and WP8 is Windows NT based, so that only leaves Blackberry's QNX-based OS as a relatively successful mobile platform whose internals are potentially optimized for embedded needs.

Generally, Android feels like a resource hog. It has the random slowness issue (everything runs fine, then suddenly everything slows down to a crawl for a couple of seconds, then everything is fine again), it consumers lots of battery, it occupies a ton of space because it needs seperate physical partitions for programs and user files like back in the days of old Unix (this is why the Galaxy S4 has so little user space, the rest of the internal storage is for apps).

Again, once you have played with the old generation of mobile OSs which were truly optimized for slow processors, small amounts of storage, and long battery lives, all newer mobile OSs feel like a waste of resources.

The main issue with Android is that it makes the inadequacy of using desktop kernels in embedded systems more obvious, by letting users and software take advantage of low-level features which are particularly ill-designed for modern needs, such as multitasking.

Also, Android is often scaled down to lower-end hardware than iOS and WP8, which further emphasizes the serious task prioritization and performance issues that its Linux internals exhibit. If iOS provided developers with similar access to its low-level functionality, you could bet that the situation would not be much different from the Android one.